Adjustable polarized reed relay



ADJUSTABLE POLARIZED REED RELAY Filed April 25. 1969 N 5 v N v s a a m;15 14 15 14 \I \I I -7&4. Fla. 5.

INVENTOR United States Patent Office 3,531,743 ADJUSTABLE POLARIZED REEDRELAY Emanuel Frydman, London, England, assignor to TelephoneManufacturing Company Limited Filed Apr. 25, 1969, Ser. No. 819,393Claims priority, application Great Britain, May 2, 1968, 20,892/ 68 Int.Cl. H01h 51/28 US. Cl. 335-153 4 Claims ABSTRACT OF THE DISCLOSURE Apolarized relay wherein the polarizing magnet is adjustable relative tothe relay pole pieces so as to aifect the bias effect on said polepieces.

This invention relates to polarised electromagnetic relays employingencased reed contacts, and more particularly changeover contacts.

In such relays it is usual to provide means for adjusting thesensitivity and/or mark-to-space balance of the contact and thisadjustment is sometimes effected by applying selective demagnetisingfields to the relay after the relay is sealed into its can. This canprovides a magnetic shield for the relay to prevent its being affectedby the operation of adjacent relays of various types. The presence ofthe shielding can tends to complicate the adjustment.

The object of the present invention is to provide a polarised sealedreed changeover contact relay using a bar magnet as the polarisingmeans, which is both simple and accurate in adjustment.

According to the invention there is provided an elec tromagnetic relaycomprising an operating coil, a sealed reed contact unit housed withinsaid operating coil and having first and second contact posts projectingoutwardly from said coil a polarising bar magnet positioned with itsopposite pole faces respectively adjacent said first and second contactposts, spring means having two parts respectively engaging said magnetattwo points spaced along the magnetic axis thereof, and adjusting meansarranged to adjust the position of one of the parts of said spring meansin the direction of said magnetic axis so as to vary the position ofsaid magnet relative to said contact posts. I

The various features and advantages of the invention will be apparentfrom the following description of an exemplary embodiment thereof takenin conjunction with the accompanying drawings in which:

FIG. 1 is a plan view of the magnet and adjusting means of a relayembodying the invention with the screening can removed,

FIG. 2 is a sectional view of part of the relay of FIG. 1,

FIG. 3 is a section of the complete relay enclosed in its screening can,

FIG. 4 shows the magnet adjusted to achieve a balanced both-side stablecondition of the changeover contact, and

FIG. 5 shows the magnet adjusted to achieve a one-side side stableposition of the changeover contact.

Referring now to FIGS. 2 and 3, a moulded support member 1 is providedwith two upstanding portions 2 and 3 on one face thereof and a hollowcore section 4, which provides both a housing for an encapsulated reedcontact 5 and a bobbin for an operating coil 6.

The upstanding portion 2 is provided with a screwthreaded bore toreceive a magnet fixing screw 7 the end of which bears against abar-shaped permanent magnet 8.

The upstanding portion 3 is provided with screwthreaded hoses to receivea spring fixing screw 9 and a spring adjusting screw 10 respectively. Agenerally U- shaped leaf spring 11 is held firmly in place againstupstanding portion 3 by means of spring fixing screw 9. The two limbs ofthe U-shaped spring are bent inwards towards each other such that, withthe spring adjusting screw 10 left loose, the ends of the spring 11 bearon the bar magnet 8 to retain the said bar magnet in position. Anadditional spring stiffening member 12, which is initially slightlybow-shaped such that its two ends are in contact with one limb of theleaf spring 11, helps the action of adjusting screw 10, when tightened,in such a manner that greater force is exerted on the bar magnet 8 bysuch, one limb of the leaf spring 11.

The position of the bar magnet 8 may now be adjusted over a fairly largerange of movement provided that, with the leaf spring 11 untensioned bythe adjusting screw 10, the magnet is well to the right of its centreposition (similar to the position shown in FIG. 5).

An electrically insulating strip 13 is inserted between the bar magnet 8and the two contact posts 14, 15, of the encapsulated reed contact 5.The polarising effect of the bar magnet 8 on the reed contact, and hencethe sensitivity of the complete relay at its coil 6, is controlled byvarying the effective thickness of the insulating strip 13. Typically,the required spacing has been found to be in the order of 0.004" andthis is conveniently obtained by sticking two strips of 0.002" thickself-adhesive polyester film to the magnet face.

Once the sensitivity and bias have been adjusted, the magnet fixingscrew 7 is tightened against the magnet face such that the magnet andinsulating strip 13 are trapped between the screw 7 and the two contactposts 14, 15, which, in turn, bear against the inner face of upstandingportion 3. This effectively stiifens the contact posts 14, 15, bypreventing flexing or bending thereof, and also tends to hold the reedcapsule firmly in the adjusted position.

Alternatively, a locking varnish or encapsulant may be used to maintaineither or both the magnet 8 and the reed capsule 5 in position.

FIG. 3 shows a section of the completed relay, now surrounded on atleast five of the six sides by a magnetic shield made, for example, froma high permeability ferrous material. The remaining open side (notshown) of the box formed by the shield is conveniently formed from asheet of insulating material into which the coil and contact lead-outpins are inserted.

The box-like structure formed by the shield 16 can be completely filledwith a thermoplastic or thermosetting resin such as Araldite (registeredtrade mark).

Two types of changeover action are used in the art; a balancedboth-side-stable contact section in which the moving spring contactremains in contact with the particular fixed contact to which it waslast moved and a one-side stable contact action in which the movingcontact always returns to a particular one of the fixed contacts onremoval of the energising current in the coil 6.

In the both-side stable condition, the bar magnet 8 has to be adjustedso that the currents required in the coil to pull the moving contactaway from each of the fixed contacts are the same or at leastsubstantially the same. This condition, therefore, is referred to asbalanced.

In a bar magnet, the theoretical pole centre lies within the boundariesof the magnet and the two pole centres are denoted by X in FIGS. 4 and5. In FIG. 4, which depicts the balanced both-side-stable adjustment,the pole centres X are approximately symmetrical with the contact postsbut the actual position for balance is large ly determined by thevarious magnetic unbalances in the reed contact and surrounding magneticstructures.

Patented Sept. 29, 1970 FIG. shows the North pole centre X oppositetocontact post 15, and the South pole centre X remote from contact post14. This gives the position where the magnetisation flux density incontact post 15 is at its maximum and the flux density in contact post14 is substantially lower. This position of the bar magnet makes thechangeover contact one-side-stable; in this case the lever contact restsagainst the contact associated with contact post 15 when no current isflowing in coil 6.

By arranging the magnet dimensions in relation .to the distance betweenthe contact posts 14, 15, and also, by arranging that there is asufficient range of adjustment catered for by leaf spring 11 andadjusting screw 10, the relay can be adjusted to be one-side-stable orboths'i'de-stable at will. It can be appreciated from FIGS. 4 and 5 thatthe spacing between the theoretical magnetic poles is different from(either greater or less than) the distance between the contact posts.

A further feature of the present invention is that, by arranging forsuitably located holes in the screening can 16 opposite adjusting screw10 and fixing screw 7, the relay may be adjusted or readjusted at anytime throughout its life without having to remove the relay from thecan.

Alternatively, if no further adjustment is required during life, themagnet 8 may be fixed in position by a locking varnish or the likeduring manufactures; so eliminating the need for magnet fixing screw 7.

Further simplification of assembly can be achieved by arranging for theupstanding portion 3 of the moulded support member 1 to have a shapedslot therein into which a correspondingly shaped leaf spring 11 isinserted and firmly located thereby. This eliminates the need for springfixing screw 9.

Alternative forms of spring may, of course, be used. For example twoseparate springs, either leaf or coil, may be provided, each bearing onone end of the bar magnet 8 such that the magnet assume a position whichbalances the forces of the two opposing springs, and at least one of thesprings is adjustable so as to cause movement of the magnet inaccordance with the degree of adjustment.

. Sealed reed changeover contacts are available 'in two forms; havingeither mercury-wetted or dry contacts. Generally speaking, themercury-wetted contact is used for high current working and the drycontact is used for low current working. The present invention isequally applicable to both types of contacts.

I claim:

1. An electromagnetic relay comprising an operating coil, a sealed reedcontact unit housed within said operating coil and having first andsecond contact posts projecting outwardlytrom: said coil, a polarisingbar magnet positioned with its opposite pole faces respectively adjacentsaid first and second contact posts, spring means having two partsrespectively engaging said magnet at two points spaced along themagnetic axis thereof, and adjusting means arranged to adjust theposition of one of the parts of saidspring means in the direction ofsaid magnetic axis so as to'vary the position of said magnet relative tosaid contact posts.

2. A-relay according to claim 1 wherein said spring means is a spring ofU-shape of which the junction between the limbs of the U-shape isanchored with respect to said contact posts by anchoring means and ofwhich the two limbs respectively engage opposite pole faces of said barmagnet.

3. A relay according to claim 2 wherein said operating coil is mountedon a former having a bore which receives said contact unit and an endcheek through which said contact posts project, said end cheek havingspaced apart upstanding projections defining a space therebetween toreceive said contact posts and said bar magnet, said anchoring meansbeing arranged to anchor said spring to one of said upstandingprojections.

4. A relay according to claim 3 including a securing screw acting in a,screw threaded bore through one of said upstanding projections to presssaid bar magnet in a direction to clamp said contact posts between theother of said upstanding projections and said bar magnet.

References Cited UNITED STATES PATENTS 3,164,698 1/1965 Perrine 335-58 X3,359,455 12/1 967 Koda et al. 335207 X B. A. GILHEANY, Primary ExaminerR. N. ENVALL, 1a., Assistant Examiner US. Cl. XR.

